1. Field of the Invention
The present invention relates generally to a drying apparatus for removing moisture from substances in liquid state, fluid state or semi-fluid state. More specifically, the invention relates to a drying apparatus having a vertically oriented rotary spiral for effectively removing moisture from the liquid state, fluid state or semi-fluid state substances.
2. Description of the Related Art
As is well known, there have been employed in various fields of industries various drying processes for drying and removing moisture from liquid state, fluid state, semi-fluid state, powder state or grain state substances. In the various sites, a variety of drying apparatus have been used.
However, in the known technologies, a drying apparatus, having high efficiency is generally only applicable for specific applications or for a specific substances. In most cases, such apparatus is not at all effective for applications other than those specified. On the other hand, there are general purpose drying apparatus which have a wide range of applicability. However, these apparatus are generally low in drying efficiency, are of complicated construction, or are facilities which require high costs to operate. No drying apparatus exists in the prior art that has a high drying efficiency and a wide range, of applicability.
The commonly owned U.S. Pat. No. 5,074,057, (the '057 patent), issued on Dec. 24, 1991 proposes a drying apparatus with a rotary spiral blade. The disclosed apparatus comprises a drying vessel to hold the moisture containing substance to be dried. The vessel has a heat conduction surface on its inner wall for transmitting heat to the substance, and a circulating rotary means to put the substance in motion in the vessel. The efficiency with which the substance can be brought to the heat conduction surface is thereby inward. The circulating rotary means comprises a rotary shaft vertically extending in the vessel in the direction of gravity, and a spiral blade integrally connected to and wound around the rotary shaft. The spiral blade has a flat upper surface, whereby rotation of the rotary shaft and hence the spiral blade causes the substance to rise up in the direction opposite of gravity. The substance slides on the flat upper surface of the spiral blade as it is being raised until the substance falls down in the direction of gravity through a falling space which is defined in the drying vessel, or until the substance comes in contact with the heat conduction surface.
With the construction set forth above, the moisture containing substance is put in the drying vessel, and then the substance is located at the lower position, under the influence of gravity. The heat conduction surface of the drying vessel is heated so that the heat is transferred to the moisture containing substance in the drying vessel. The spiral blade rotates about its axle. In the case where the spiral blade is hollow, a heating medium is led into the inside of the spiral blade, to heat the upper surface of the spiral blade so that it will also function as a heat conduction surface just like the inner wall of the drying vessel.
The moisture containing substance circulates in the '057 patent, at an increased speed and brings the substance into contact with the heat conduction surface of the drying apparatus at an increased efficiency. Thus, this drying apparatus achieves both a high drying efficiency and a wider range of application. However, there is still room for improvement in the '057 patent.
For example, in the prior proposed invention, the moisture containing substance is transported from the lower portion of the drying vessel, toward the upper portion, on the flat upper surface of the spiral blade, which also serves as a part of the heat condition surface. The substance travelling along the flat upper surface of the spiral blade forms a thin film contacting with the heat conduction surface for promoting heat transfer from the heat conduction surface to the substance. As set out above, in the construction set forth above, for obtaining a satisfactorily level of removal of the moisture from the substance, it is necessary to smoothly shift the substance along the flat upper surface of the spiral blade. To achieve this, the substance approaching the upper portion of the drying vessel needs to fall down from the spiral blade to repeat the heating cycles.
The present invention is thus intended to provide an improvement for applicant's prior invention so as to achieve a smooth circulation of the moisture containing substance and to assure that the substance will fall down once it reaches the top end of the spiral blade.